Best AR-15 Calibers Compared (2026): From 5.56 to .450 Bushmaster

Last updated March 28th 2026

Some of the links below are affiliate links, meaning at no additional cost to you, we may earn a commission if you click through and make a purchase.

Introduction: Best AR-15 Calibers in 2026

The AR-15 platform is basically the LEGO of the gun world. Swap an upper receiver and you’ve got a completely different rifle shooting a completely different caliber. That’s the beauty of it. One lower, a dozen possibilities.

I’ve built ARs in just about every caliber on this list over the years, and I’ll tell you straight up: there’s no single “best” caliber. There’s the best caliber for what you’re doing. A 300 Blackout makes zero sense if you’re shooting coyotes at 400 yards. And a 6.5 Grendel is overkill (and over-cost) for punching paper at the indoor range.

So let’s break down the eight most popular AR-15 calibers, what each one actually does well, and where the money makes sense. If you’re building your first AR, start with the standard 5.56. If you’re adding a second upper to your collection, this guide will help you figure out which direction to go. Check out our best AR-15 rifles guide for complete rifle recommendations, or our AR-15 build guide if you want to put one together yourself.

---

1. 5.56 NATO / .223 Remington: The Default Choice

• Best For: General purpose, home defense, target shooting, varmint hunting
• Effective Range: 500 yards (600+ with 77gr match ammo)
• Barrel Length Sweet Spot: 16″ (14.5″ with pinned muzzle device)
• Ammo Cost: $0.28-0.35/round (steel case as low as $0.22)
• Suppressor Compatibility: Good, but supersonic crack remains
• Twist Rate: 1:7 or 1:8 for versatility

This is where everyone starts, and honestly, most people never need to leave. The 5.56 NATO (and its slightly lower-pressure cousin, the .223 Remington) is the standard AR-15 cartridge for a reason. Ammo is dirt cheap compared to everything else on this list. You can find brass-cased 5.56 for around 30 cents a round, and steel case stuff goes even lower.

I’ve got three different 5.56 uppers and they all serve different purposes. A 16″ midlength for general range work, a 14.5″ with a pinned Surefire brake for a lighter carry setup, and a 20″ HBAR that I use for precision work out to 600 yards. The cartridge is that versatile. Want to shoot cheap? Load up some 55gr ball ammo. Want to reach out? Throw some 77gr Sierra MatchKings in there.

The only real limitation is terminal performance on larger game. Most states won’t let you hunt deer with .223/5.56, and even where it’s legal, it’s marginal at best. For everything else, including home defense, target shooting, varmint control, and competition, 5.56 is king. And the ammo prices mean you can actually afford to practice.

Best For: First-time AR buyers, general purpose use, anyone who wants to shoot a lot without going broke. It’s the Honda Civic of calibers. Not flashy, but it just works.

---

2. 300 Blackout: The Suppressor King

• Best For: Suppressed shooting, home defense, hog hunting, short barrels
• Effective Range: 300 yards (supersonic), 200 yards (subsonic)
• Barrel Length Sweet Spot: 9″ (burns all powder efficiently)
• Ammo Cost: $0.70-1.00/round
• Suppressor Compatibility: Excellent. Subsonic loads are hearing-safe
• Twist Rate: 1:7 or 1:8 (needs 1:7 for heavy 220gr subs)

If 5.56 is the practical choice, 300 Blackout is the fun choice. There’s nothing quite like shooting a suppressed 300 BLK SBR with subsonic ammo. It sounds like a loud stapler. Seriously. Your neighbors won’t even know you’re at the range.

The genius of 300 Blackout is that it was designed from the ground up for short barrels and suppressors. A 9″ barrel burns all the powder in the cartridge, meaning you get full ballistic performance from a tiny package. Compare that to 5.56, where a 10.5″ barrel wastes a ton of powder in a giant fireball. The 300 BLK also hits way harder inside 200 yards. We’re talking .30 caliber projectiles at 1,000+ fps (subsonic) or 2,200+ fps (supersonic). For the best 300 Blackout rifles, check our dedicated guide.

Here’s the thing though. Ammo is expensive. You’re looking at 70 cents to a dollar per trigger pull, and the good subsonic hunting loads run even more. You also need to be extremely careful if you own both 5.56 and 300 BLK uppers. A 300 Blackout round will chamber in a 5.56 barrel, and if you pull that trigger, it’s a catastrophic failure. Label your magazines. Color code them. Tattoo it on your forehead if you have to.

Best For: Suppressed shooting enthusiasts, home defense (with the right loads), hog hunting at close range. If you already have a 5.56 and want a second upper that does something completely different, this is the move.

---

3. 6.5 Grendel: The Long-Range Hammer

• Best For: Long-range precision, medium game hunting (deer, antelope)
• Effective Range: 800+ yards
• Barrel Length Sweet Spot: 20-24″
• Ammo Cost: $0.90-1.30/round
• Suppressor Compatibility: Good
• Twist Rate: 1:8

Want to shoot far without stepping up to an AR-10? The 6.5 Grendel is your answer. This caliber turns the lightweight AR-15 platform into a legitimate 800+ yard precision rifle. The high ballistic coefficient of 6.5mm bullets means they buck wind better and retain energy further downrange than anything else you can stuff into an AR-15 magazine.

I built a Grendel upper on an Aero Precision platform with a 20″ barrel, and it consistently prints sub-MOA groups at 100 yards with Hornady Black ammo. At 600 yards, it’s still holding about 2 MOA, which is more than acceptable for steel. The Grendel also carries enough energy to ethically harvest deer out to 300 yards or so, making it a legitimate hunting round. For more options, see our 6.5 Grendel AR-15 guide and our 6.5 Creedmoor semi-auto rifles for the AR-10 alternative.

The downsides are real though. You need a different bolt (the bolt face is larger than 5.56), so it’s not a simple barrel swap. Ammo runs about a dollar a round for decent stuff, and good luck finding it at your local sporting goods store. You’ll be ordering online. Magazine compatibility can also be hit or miss depending on your lower.

Best For: Long-range shooters who want to stay on the AR-15 platform, hunters who want one rifle that shoots far and hits hard enough for deer-sized game.

---

4. 6.8 SPC: The Military’s Almost-Replacement

• Best For: Medium game hunting, enhanced terminal performance over 5.56
• Effective Range: 500 yards
• Barrel Length Sweet Spot: 16-18″
• Ammo Cost: $1.00-1.50/round
• Suppressor Compatibility: Good
• Twist Rate: 1:10 or 1:11

The 6.8 SPC has a cool backstory. It was developed by U.S. Special Operations as a replacement for the 5.56 NATO, designed to hit harder at intermediate ranges without giving up the AR-15 platform. It never got adopted military-wide (the Army went with 6.8×51 instead, which is a completely different beast), but it found a solid niche in the civilian market.

Where the 6.8 SPC shines is hunting. It delivers about 40% more energy than 5.56 at 300 yards, which makes it a legitimate deer and hog caliber without stepping up to a heavier, more expensive platform. The recoil is noticeable but very manageable. Think of it as a beefed-up 5.56 that hits like a truck at medium range.

The problem? It’s a dying breed. The 6.5 Grendel does the long-range thing better, and the newer 6mm ARC is stealing its lunch money in the precision space. Ammo selection is shrinking, prices are climbing, and fewer manufacturers are making complete rifles in 6.8 SPC. If you already own one, great. If you’re buying new, I’d steer you toward the Grendel instead.

Best For: Hog hunters who want more punch than 5.56 without going big-bore, and anyone who already has a 6.8 SPC setup and loves it. Not the best choice for a new build in 2026.

---

5. .350 Legend: The Straight-Wall Deer Slayer

• Best For: Deer hunting in straight-wall cartridge states (OH, IN, IA, MI)
• Effective Range: 200-250 yards
• Barrel Length Sweet Spot: 16-20″
• Ammo Cost: $0.80-1.20/round
• Suppressor Compatibility: Good
• Twist Rate: 1:16

If you hunt deer in Ohio, Indiana, Iowa, or Michigan, you already know the pain. These states require straight-wall cartridges for rifle hunting. For years, that meant lever-action rifles in .357 or .44 Magnum. Then Winchester came along with the .350 Legend and suddenly, AR-15 hunters in those states had a real option.

The .350 Legend pushes a .355-caliber bullet at around 2,300 fps from a 16″ barrel. That’s enough to cleanly take whitetail out to 200 yards, which covers the vast majority of Midwest deer hunting scenarios. The recoil is also hilariously light for a deer cartridge. My buddy’s 12-year-old son shoots a .350 Legend AR and barely flinches. Try that with a .30-06.

Outside of straight-wall states, the .350 Legend doesn’t make a ton of sense. You’d be better off with 6.5 Grendel or even just a bolt gun in .308. But for its intended purpose, it’s basically perfect. Winchester really nailed this one. Check out our best AR-15s for hunting for complete rifle recommendations in this caliber.

Best For: Midwest deer hunters in straight-wall only states. If that’s you, stop reading and go buy one. If it’s not you, keep scrolling.

---

6. .450 Bushmaster: The Thumper

• Best For: Big game hunting, straight-wall states, maximum stopping power
• Effective Range: 250 yards
• Barrel Length Sweet Spot: 16-20″
• Ammo Cost: $1.30-2.00/round
• Suppressor Compatibility: Fair (still very loud)
• Twist Rate: 1:24

Tim LeGendre of LeMag Firearms had a vision: stuff the biggest, nastiest round possible into an AR-15 magazine well. The result was the .450 Bushmaster, and it hits like a freight train. We’re talking a 250-grain bullet at 2,200 fps. That’s more muzzle energy than a .30-06. From an AR-15. Let that sink in.

I won’t sugarcoat it: the recoil is punishing. First time I shot a .450 Bushmaster AR, it rocked me back on my heels. It’s a completely different experience from shooting 5.56. You’re not going to do rapid follow-up shots. You’re not going to run through 200 rounds at the range for fun. This is a purpose-built hunting tool.

And for that purpose, it’s outstanding. This round will put down anything in North America. Deer, elk, black bear, hogs. One well-placed shot and the animal drops. It’s also straight-wall compliant in states that require it, giving those hunters access to serious big-game performance. Ruger and Bushmaster both make solid factory rifles in .450 Bushmaster.

Best For: Big-game hunters who want an AR platform, straight-wall state hunters who need maximum power, and anyone who just wants the biggest boom possible from a standard AR-15 lower.

---

7. .224 Valkyrie: The Precision Play

• Best For: Long-range precision, competition, 1,000-yard shooting from AR-15
• Effective Range: 1,000+ yards (stays supersonic past 1,300 yds)
• Barrel Length Sweet Spot: 22-24″
• Ammo Cost: $1.00-1.50/round
• Suppressor Compatibility: Good
• Twist Rate: 1:7

Federal designed the .224 Valkyrie to do one thing: stay supersonic past 1,000 yards from an AR-15 platform. Mission accomplished. With a 90-grain Sierra MatchKing bullet, this cartridge remains supersonic past 1,300 yards. That’s nuts for something that fits in a standard AR-15 magazine well.

The reality on the ground is more complicated. Barrel life is short (around 3,000 rounds before accuracy degrades noticeably), ammo options are limited, and the caliber never gained the widespread adoption that Federal hoped for. It landed in this awkward space where 6.5 Grendel does most of the same things with better ammo availability, and serious precision shooters just step up to an AR-10 in 6.5 Creedmoor anyway.

That said, if you’re specifically interested in 1,000-yard shooting and want to keep your gun light and AR-15 sized, the Valkyrie is still the best option. Just know that you’re committing to a niche caliber with niche ammo availability. Ordering online is basically mandatory.

Best For: Dedicated precision shooters who want maximum range from the AR-15 platform. If you’re going to shoot 1,000+ yards regularly, the Valkyrie delivers. Everyone else should probably go Grendel.

---

8. .22 LR: The Training Partner

• Best For: Training, plinking, teaching new shooters, small game
• Effective Range: 75 yards (practical), 150 yards (max)
• Barrel Length Sweet Spot: 16″ (matches standard AR profile)
• Ammo Cost: $0.05-0.08/round
• Suppressor Compatibility: Excellent (already quiet)
• Options: Conversion kit ($200-300) or dedicated .22 LR upper/rifle

This one’s a cheat code. Grab a CMMG .22 LR conversion kit for about $200, drop it into your existing 5.56 upper (takes about 10 seconds), and suddenly you’re shooting 7-cent rounds instead of 30-cent rounds. Do the math on a 500-round range day. That’s $35 instead of $150. You’re welcome.

I keep a CMMG conversion in my range bag at all times. It’s the first thing that goes into the rifle when I’m working on fundamentals, trigger control, or teaching someone new to shoot. The manual of arms is identical to a standard AR-15, so all the training transfers directly. The only difference is you’re not flinching from recoil or wincing at the cost.

You can also buy dedicated .22 LR AR-15s from companies like Smith & Wesson (M&P 15-22) or Tippmann. These are more reliable than conversion kits since they’re purpose-built, but they’re a separate gun rather than a drop-in solution. Either way, having a .22 LR option for your AR platform is one of the smartest investments you can make. If you’re looking for a full rifle, check out our best AR-15 rifles roundup.

Best For: Every single AR-15 owner. Seriously. If you don’t have a .22 conversion kit yet, you’re burning money every time you go to the range. Buy one today.

---

Buyer’s Guide: How to Choose the Right AR-15 Caliber

Match the Caliber to Your Mission

Here’s the simple framework I use. Ask yourself one question: “What am I going to do with this rifle?” Your answer determines your caliber. Home defense and general range use? 5.56. Suppressed SBR? 300 Blackout. Long-range precision? 6.5 Grendel or .224 Valkyrie. Deer hunting in a straight-wall state? .350 Legend. Big game? .450 Bushmaster. Training on the cheap? .22 LR conversion.

Don’t overthink it. I’ve seen guys spend six months on Reddit agonizing over caliber choice when they should have just built a 5.56 and started shooting. You can always add a second upper later. That’s the whole point of the AR-15 platform.

Ammo Cost and Availability Matter

This is the factor most people underestimate. A gun you can’t afford to feed is a gun that sits in the safe. At current prices, you can shoot 5.56 all day for about $150 in ammo. A comparable range day in .450 Bushmaster would run you $400+. That difference adds up fast.

I also strongly recommend sticking with calibers you can actually find ammo for. Walking into a gun store and finding 5.56 or .300 Blackout on the shelf is easy. Finding .224 Valkyrie or 6.8 SPC in stock? Good luck. Online ordering solves this, but you’ll want to keep a healthy supply on hand. Check our best AR-15 ammo guide for 5.56/.223 ammo picks.

The “One AR-15” Caliber

If you’re only going to have one AR-15 caliber for the rest of your life, it’s 5.56 NATO. Full stop. It does everything well enough, ammo is cheap enough to train with regularly, it’s available everywhere, and it’s the standard that every accessory and magazine is designed around. Start there. Get good with it. Then branch out.

If you can have two calibers, add a 300 Blackout upper if you care about suppressed shooting, or a 6.5 Grendel upper if you want long-range capability. Either way, your second caliber should complement what 5.56 already does, not duplicate it.

Browse All AR-15 Parts & Upgrades →

FAQ: Best AR-15 Calibers